BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Sorghum halepense | Johnson Grass 



GENERAL BOTANICAL CHARACTERISTICS : 
Johnson grass is an exotic, warm-season, rhizomatous, perennial
graminoid.  Its stems are typically 1.5 to 4.5 feet (0.5-1.5 m) high,
occasionally reaching heights of 6 to 7 feet (3-3.3 m) [14,16].  Its
purplish panicles are 4 to 12 inches (10-30 cm) long, and leaves are 4
to 20 inches (10-50 cm) long [24].  Rhizomes can be as much as 0.5
inches (1 cm) in diameter and 6 feet (2 m) long [35].  The awned, ovoid
seeds are brown [16].


RAUNKIAER LIFE FORM : 
   Geophyte
   Phanerophyte


REGENERATION PROCESSES : 
Johnson grass recolonizes both by seed and from extensive, creeping
rhizomes [16,24].  Rhizomes can be as deep as 15.7 to 19.7 inches (40-50
cm); the bulk of the rhizomes are found 9.8 inches (25 cm) below the
soil surface [36].  McWhorter [22] found rhizomes in clay in the top 3
inches (7.5 cm) of soil, and rhizomes growing in sandy loams were in the
top 5 inches (12.5 cm) of soil.  Rhizomes at a depth of 7.9 inches (20
cm) can be killed at temperatures below 15 degrees F (-9 deg C).
Likewise, exposure to temperatures between 86 and 95 degrees F (30-35
deg C) for 7 days can kill rhizomes [35].  Johnson grass also produces a
large quantity of viable seeds (from 540-1,440 dm3 per ha) [35].


SITE CHARACTERISTICS : 
Johnson grass invades low-elevation wet places, irrigation ditches, waste
areas, roadsides, cropfields, and other disturbed places in temperate
climates [12,16,24,35].  In Utah it is found between 850 and 1,500 feet
(259-457 m) in elevation [38].  In Arizona it can invade places as high
as 6,000 feet (1,829 m) [19].  Some associate species include honey
mesquite (Prosopis glandulosa), Texas persimmon (Diospyros texana), live
oak (Quercus fusiformis), eastern cottonwood (Populus deltoides), willow
(Salix spp.), Mexican elder (Sambacus), Douglas sagewort (Artemesia
douglasiana), horsetail (Equisetum spp.), sedge (Carex spp.), ragweed
(Ambrosia spp.), smartweed (Polygonum spp.), devilweed aster (Aster
spinosus), hardstem bulrush (Scirpus acutus), sweetclover (Melilotus
spp.), and panic grass (Panicum spp.)  [8,17,29,34].  Some crop species
invaded by Johnson grass include corn (Zea mays), alfalfa (Malidago
spp.), grapes (Vitis spp.), and cotton (Gossypium spp.)[16].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Johnson grass invades native grasslands subjected to unnatural frequent
flooding [17].  It is early successional in riparian types of California
[8].  Johnson grass can sometimes be dominant with shrubs in Oklahoma
tallgrass prairies [7].


SEASONAL DEVELOPMENT : 
Flowering dates for Johnson grass have been recorded for May through
November [14,19,24].  Flowering in Johnson grass is highly dependent on
temperature, while water availability and nitrogen concentration do not
have much effect [5].

Related categories for Species: Sorghum halepense | Johnson Grass